Multiple sclerosis (MS), a chronic demyelinating disease of the central nervous system, is a major cause of neurological disability in Western countries. In spite of intensive and sustained research efforts, existing treatment options do not substantially prevent tissue damage and clinical disability. MS is increasingly recognized as an autoimmune neurodegenerative disease triggered by inflammatory attacks of the CNS. We propose to study a newly synthesized molecule (O-1966) that may significantly reduce the contribution of immune cells to CNS damage. O-1966 is a member of the cannabinoid class of molecules. While cannabinoids derived from the plant Cannabis Sativa have been used for thousands of years, their value in the treatment of diseases such as MS has been limited by their psychoactive properties. Presently, it is possible to target the CB2 receptors, primarily expressed on immune cells, which exhibit immunomodulatory functions. O-1966, a selective CB2 agonist, alters immune functions without psychoactive effects. Preliminary results showed that stimulation of CB2 receptors decreases CNS damage in experimental autoimmune encephalomyelitis (EAE). Our preliminary data suggest that the protective action of O-1966 in EAE occurs through effects on inflammation. In this proposal we will investigate the molecular mechanisms by which O-1966 specifically influences the function of immune cells. The proposed studies will be conducted at both molecular/cellular and whole animal level, to allow a better evaluation of the therapeutic potential of O- 1966. We propose that CB2 receptor activation by the selective CB2R agonist O-1966 results in: 1. changes in the phenotype of effector T cells through the induction of regulatory T cells;and 2. inhibition of encephalitogenic T cell traffic to the CNS through a reduction in T cell rolling and adhesion to the vascular CNS endothelium. In Specific Aim 1 we will evaluate the effect of O-1966 in EAE and characterize the CNS infiltrating cells, based on the hypothesis that CB2 activation results in a shift in T cell differentiation from encephalitogenic Th17/Th1 to regulatory T cells. Based on preliminary studies, we propose that the CB2 selective agonist O-1966 affects T cell differentiation through the induction of tolerogenic dendritic cells. This represents a new research area, since the role of cannabinoids on DC differentiation has not been addressed. In Specific Aim 2 we will examine the effects of O-1966 on encephalitogenic Teffector and Treg cell rolling and adhesion to CNS postcapillary venules by intravital microscopy, its effect on the expression of adhesion molecules in Teff/Treg cells and in CNS endothelial cells, and on the expression of chemokines involved in the recruitment of activated T cells to the perivascular space and CNS parenchyma. The identification of molecular/cellular factors and of the mechanisms involved in the anti-inflammatory effect of CB2 receptor ligands will have a significant impact on the understanding and intervention in CNS autoimmune/inflammatory diseases. The ultimate goal of this proposal is the development of new effective therapeutic agents targeted at modification of the inflammatory responses that contribute to MS.